This invention relates to a control system for an electric motor, which is arranged to drive a rope drum of a mine winder or a similar hoist system.
A mine winder or hoist usually employs an electric motor which is connected to at least one rope drum, and commonly two rope drums. A cage or conveyance is attached to the free end of a rope which is wound on the drum, so that rotation of the drum raises or lowers the conveyance in a mine shaft. Usually, the winding arrangement is such that one conveyance is raised as the other is lowered.
Deep mine shafts, such as those encountered in the gold mining industry, necessitate long rope lengths. In such systems, oscillations are induced in the flexible system comprising the conveyances, ropes, the inertia of the motor and winding drums, and possibly other travelling masses in the system. Such oscillations are excited, in particular, by winding drum accelerations which occur during normal winding and during emergency braking. The effect is a longitudinal dynamic displacement of the cage at the end of the rope with an undesirably large amplitude, which causes increased tensile loading of the rope. This necessitates the use of a stronger rope than would be required for steady-state operation, increasing the mass and cost of the rope and limiting the attainable shaft depth.
It is an object of the invention to provide a control system for normal operation and emergency braking which reduces the longitudinal oscillations.